Wellbores drilled into subterranean formations may enable recovery of desirable fluids (e.g., hydrocarbons) using a number of different techniques. Knowing the location of a target wellbore may be important while drilling a second wellbore. For example, in the case of a target wellbore that may be blown out, the target wellbore may need to be intersected precisely by the second (or relief) wellbore in order to stop the blow out. Another application may be where a second wellbore may need to be drilled parallel to the target wellbore, for example, in a steam-assisted gravity drainage (“SAGD”) operation, wherein the second wellbore may be an injection wellbore while the target wellbore may be a production wellbore. Yet another application may be where knowledge of the target wellbore's location may be needed to avoid collision during drilling of the second wellbore.
Electromagnetic induction tools disposed on bottom hole assemblies may be employed in subterranean operations to determine direction and distance between two wellbores. Electromagnetic induction tools may use different techniques to obtain current on a conductive member in the target wellbore. Approaches may include directly injecting a current into the conductive member and/or inducing a current on a conductive member by transmitting electromagnetic fields by coil antennas positioned in a second wellbore. The injection of current from the electromagnetic induction tools may induce a current along the bottom hole assembly, which may create a direct signal. The direct signal may be sensed and recorded by a receiver disposed on the bottom hole assembly. Recording the direct signal may hinder and/or overshadow secondary signals recorded from a formation and/or target wellbore. Gap subs may be implemented to prevent the propagation of direct signals along the bottom hole assembly. Specifically, gap subs may prevent current from flowing through a section of the bottom hole assembly. In examples, controls may be implemented to control the movement of voltage and/or current through the gap sub, which may allow an operator to cancel out current at any position along the bottom hole assembly.